Optical and Structural Characterization of Arsenide/Phosphide Interfaces Formed by Flow Modulation Epitaxy
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lasers with wavelengths spanning from the visible to the infrared. Because of the technological importance of this system, it is essential to develop a good understanding of the formation of heterostructures on both GaAs and InP substrates as well as to develop tools for assessing and optimizing arenide to phosphide (As/P) interface formation and overall structural and optical quality. In this report, we discuss the growth, characterization and optimization of both lattice matched and strained GaAsP/GaInP heterostructures on GaAs substrates and compare the As/P transition as made on GaAs and InP substrates. RESULTS & DISCUSSION Experimental Technique Bulk layers, single -quantum wells (SQWs), and superlattices (SLs) were grown at 530°C-600°C using Elow Modulation Epitaxy (FME? at 76 torr in a vertical barrel Organometallic Yapor Phase Epitaxy (OMVPE) system. The sources were triethylgallium, trimethylindium, arsine and phosphine. The details of the interface formation have been discussed previously and will be noted here only as an aid to the discussion. 2' 3 Composition subscripts will be omitted from the ternary materials GaAsP, GaInP, and GaInAs where not crucial to the discussion. All GaInP and GaInAs layers are lattice matched unless otherwise noted. Throughout the discussion, 'well' ('barrier') will be used to refer to the GaAsP (GaInP). Further, 'As/P' will refer to both the arsenide to phosphide and phosphide to arsenide transitions. 387 Mat. Res. Soc. Symp. Proc. Vol. 405 01996 Materials Research Society
Symmetric (004) and asymmetric {2241 double grystal x-ray diffraction (DCXRD) are used to measure the state of strain in and composition of the samples as well as the period of the SLs. DCXRD (004) full-width at half-maximum values varied with composition and strain and ranged from 50-250 arc sec for the bulk samples and from 60-80 arc sec for the SLs. The ternary elastic constants were linearly interpolated from those of the endpoint binaries for calculation of composition from mismatch. Raman scattering is employed to provide a complimentary estimate of the composition of the thin GaAsP layers in the SLs and is used in combination with DCXRD to assess the structural quality of the heterostructures. Low temperature photoluminescence (1K PL) is utilized to qualitatively assess the chemical composition of the heterointerfaces and to measure ground state optical transitions in the SQWs and SLs. Transmission electron microscopy (TEM) is employed to verify layer thicknesses in the thin, strained layers as well as to examine interface abruptness and smoothness. In addition, atomic force microscopy (AFM) is used to examine surface morphology of selected samples. Bulk Layers Two well and two barrier materials were employed in this study: GaAsP and GaInP on GaAs and GaInAs and InP on InP. AFM images of pseudomorphic GaAs 0.95P0 .05 and GaInP grown at 530'C are shown in Fig. la and lb, respectively. Both are characterized by rough surfaces, with random height variations of 50A. on the GaAsP and 30A on the GaInP.
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